1. Priority Claim
Priority is claimed for this invention and application, a corresponding application having been filed in Germany on May 16, 2002, No. 102 21 833.1-12.
2. Field of the Invention
The invention relates to a self-pumping, hydropneumatic suspension strut unit with an internal level control.
3. Description of the Related Art
Self-pumping hydropneumatic suspension strut units with internal level control intended for use in passenger vehicles are known in the art, for example in DE 198 36 487 A1. A passenger vehicle of this type has a suspension, which typically includes a suspension spring and a shock absorber. When it is desired to use a self-pumping hydropneumatic suspension strut unit, the normal suspension spring is replaced by a weaker suspension spring, since most of the useful load in a passenger vehicle will be carried and controlled by the self-pumping hydropneumatic suspension strut unit.
A suspension strut unit of this type has a pump rod which is mounted in the hollow piston rod and an inlet valve and an outlet valve so that, as a result of relative motion between the body of the vehicle and the vehicle axle, a damping medium is pumped from a low-pressure space into a high-pressure space. These two spaces are partially filled with oil and gas. For diffusion, on the high-pressure side a partition element separates the oil from the gas. When the pump is operating as a result of irregularities in the road surface, the pressure in the high-pressure chamber increases while the pressure in the low-pressure chamber decreases, as a result of which, the piston rod is pushed outward. When the vehicle body reaches the desired level, a bypass insures that the vehicle body will be unable to move any further.
Disadvantageously, suspension strut units are not designed for commercial vehicles (e.g. small delivery trucks, etc.) equipped with leaf-spring suspensions and used to transport heavy useful loads. In such commercial vehicles, the leaf spring not only guides the axle but also absorbs torque, so that reducing the strength of the leaf spring is not an option. A suspension strut unit with self-pumping, hydropneumatic internal level control, however, cannot be used with an unmodified leaf spring because the body of the vehicle would otherwise be raised far too high in the unloaded state.
Thus, it is an object of the present invention to provide a self-pumping, hydropneumatic suspension strut unit with an internal level control such that, without the need to modify the basic design of the suspension already present in the vehicle, even commercial vehicles with leaf spring suspensions designed to transport heavy useful loads can be automatically controlled to remain at predetermined ride height levels.